Method and device for splicing optical conductors

ABSTRACT

In a process of splicing optical fibers, a temperature distribution during the splicing of the waveguides at a constant discharge current will depend on ambient parameters, which include temperature, air pressure and air humidity, and these parameters also influence the quality of the splice being produced. The discharge current is regulated by measuring the actual intensity distribution of the thermionic emissions of the waveguide during the splicing operation and by comparing this intensity distribution with a stored reference intensity distribution. The device includes a sensor which is used for measuring the intensity distribution and for adjusting the ends of the waveguides relative to each other.

The invention relates to a method for splicing optical conductors byusing an arc discharge between two electrodes and controlling the arcdischarge by controlling the discharge current and to a splicing devicewhich has two electrodes, holding devices for positioning the conductorsbetween the electrodes, a current source for striking an arc dischargebetween the electrodes and a set point generator for providing a presetdischarge current for the source.

Two methods are known for connecting the optical conductors (glass orpolymer fibers) which are being increasingly used in opticaltelecommunications engineering: on the one hand, bonding ends of theoptical conductors in preassembled and standardized connectors and, onthe other hand, splicing optical conductors with prepared end faces toform a single optical conductor. When splicing the optical conductors insplicing devices, two optical conductors with prepared end faces arefastened on two holding devices which can then be moved with the aid ofadjusting devices so that the end faces are well adjusted relative toone another. After the adjustment, the two ends are then, in general,thermally welded. The thermal welding is performed in this case using anarc discharge between two electrodes.

U.S. Pat. No. 4,506,947 discloses a method in which a video camera isused to adjust two glass fibers relative to one another in a controlledfashion by illuminating the splice point with ultraviolet light so thatthe core of the glass fibers, which is doped with germanium, emits lightin the visible wavelength region. The light is displayed on a monitorvia the video camera and a downstream image evaluation unit. Theoperator of the device can therefore adjust the cores of the two glassfibers relative to one another via the monitoring device and theadjusting device. The quality of the splicing operation is not observed.

The quality of a splice which is intended to achieve optical losses assmall as possible during the transmission of light from one opticalconductor into the other, depends essentially on the parameters set inthe splicing device. The discharge current used to weld the opticalconductors is also one of these parameters. In the case of optimumadjustment and constant ambient conditions (air pressure, air humidity,temperature), heating which remains good is achieved with the aid of aconstant discharge current. In the case of altered ambient conditionsand used or soiled electrodes, there is a change in the heating of theoptical conductors even given a constant discharge current, and thus achange in the quality of splicing.

In the field of material processing of work pieces using lasers, DE 19617 388 discloses a method which uses video sensors to evaluate thetemperature distribution in a plasma initiated by a laser. The plasmacorresponds to the arc discharge during splicing, but the method canprovide no information either on the temperature distribution in theoptical conductor itself, or thus on the quality of the splice.

SUMMARY OF THE INVENTION

It is therefore the object of the invention to automate the control ofthe temperature for a splicing operation independently of ambientparameters.

The object is achieved by means of a method and a splicing device of thetype mentioned at the beginning by using a sensor to measure the actualintensity distribution occurring during splicing, storing a referenceintensity distribution in a storage device, comparing the measuredintensity distribution with the reference intensity distribution andcorrecting the discharge current in a controller in response to anydeviations therebetween.

For this purpose, the actual intensity distribution occurring in thecase of optical conductors which emit thermionically upon theapplication of a preset discharge current is measured and compared witha stored reference intensity distribution. Intensity distribution isunderstood below as a spatially resolved (if appropriate, alsowavelength-resolved) image of the ends of the optical conductors. In thecase of a deviation, the discharge current is then varied such that theactual intensity distribution attained at least approaches the storedreference intensity distribution. This results in automated control ofthe discharge current which is independent of ambient parameters, and sosplicing operations lead to identical temperature distributions in theoptical conductors, and thus to a quality of the splices which remainsgood.

The newly determined, adapted discharge current is advantageously storedas a preset discharge current for future splicing operations.

When color cameras are used, the reference intensity distribution can bestored in a wavelength-resolved fashion and compared withwavelength-resolved actual intensity distributions during the splicingoperations in order to arrive at a more accurate statement on thetemperature distribution in the optical conductors.

When black and white cameras are used gray-scale values areadvantageously assigned to the intensity distributions.

The gray-scale values determined in the process are averaged over thearea of the two optical conductors, and only this mean gray-scale valueof the actual intensity distribution is compared with a mean referencegray-scale value. The quantity of data to be stored is advantageouslyreduced by this process.

In a preferred embodiment, the gray-scale values of a row of the opticalsensor are evaluated in the direction of the axes of the two opticalconductors in a spatially resolved fashion. The actual position of aprescribed gray-scale value which occurs is compared with a storedreference position of the prescribed gray-scale value, and in the caseof a deviation the discharge current is corrected such that the actualposition approaches the reference position. The quantity of data to bestored is also reduced by this embodiment.

A temporal actual sequence of intensity distributions is advantageouslystored and compared with a stored reference sequence in order to arriveat a yet more accurate statement on the temperature distribution duringthe splicing operation.

A particularly reproducible method is achieved by virtue of the factthat the temporal sequence is triggered by the application of thedischarge current.

In the case of the splicing device, a memory is provided for storing thereference intensity distribution in order thereby to compare in acomparator the actual intensity distribution measured with the aid of asensor. A controller serves the purpose of controlling the dischargecurrent as a function of the comparison made.

For the purpose of a simple construction in conjunction with reducedcosts, the sensor is designed such that it can also be used to adjustthe ends of the optical conductors.

The invention is explained in more detail in exemplary embodiments withthe aid of the figures of the drawins.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic of the inventive splicing device for splicingoptical conductors,

FIG. 2a shows a schematic of the intensity distribution over thelongitudinal axis of the two optical conductors in the case of a firsttemperature distribution, and

FIG. 2b shows a schematic of the intensity distribution over thelongitudinal axis of the two optical conductors in the case of a secondtemperature distribution.

DESCRIPTION OF THE PREFFERRED EMBODIMENTS

In accordance with FIG. 1, for splicing purposes the end of a firstoptical conductor 1 is fastened on a first holding device 2. A secondoptical conductor 3 is fastened on a second holding device 4. Theholding devices 2, 4 also serve as adjusting devices with the aid ofwhich the two ends of the optical conductors 1, 3 can be adjusted to aminimum offset relative to one another so as to produce an additionaloptical loss which is as small as possible at the transition point(splice point) from the first optical conductor 1 to the second opticalconductor 3. The two ends of the optical conductors 1, 3 are welded toone another by striking an arc 5 between two electrodes 6. In this case,a prescribed discharge current is applied to the two electrodes 6 by acontrol device 7 which comprises a current source 10 and an assignedsetpoint generator 11.

According to the invention, the region of the arc 5 with the ends of theoptical conductors 1, 3 is picked up by a sensor 8, for example a videocamera, and evaluated in a downstream image evaluation unit 9. The imageevaluation unit 9 here comprises a storage device 13 for storing areference intensity distribution and a comparator 14 for comparing theactual intensity distribution with the reference intensity distribution.A controller 12 is driven as a function of the comparison and, for itspart, controls the discharge current via the setpoint generator 11assigned to the current source 10 in such a way that the actualintensity distribution at least approaches the reference intensitydistribution. Of course, the greatest possible approach is targeted, inorder to obtain a reproducible quality for the splice.

The sensor 8 with the downstream image evaluation unit 9 can alsoadvantageously be used to adjust the optical conductors, thus resultingin a design of the splicing device which is simplified by comparisonwith a device with two sensors.

In order to be able to measure the change in intensity, it is necessaryto dispense with an automatic gain control of the sensor 8 when applyingthe method. If the offset of the two optical conductors relative to oneanother is measured using light injected into the optical conductors,this injected light must be excluded during the splicing operation inorder for it not to influence the intensity distribution to be measured.

The reference intensity distribution has been determined, for example,during a “training phase” in which various intensity distributionsattained with the aid of various discharge currents are stored, thequality of the splices resulting therefrom is investigated, and theintensity distribution for the splice with the smallest losses issubsequently stored as a reference intensity distribution, and theassociated discharge current is stored as a preset discharge current.

Upon application of the preset discharge current, the ends of theoptical conductors begin to emit thermonic radiation in the region ofthe arc 5 and thus to emit light in the visible region of the spectrum.The temperature distribution in the optical conductors will have amaximum in the region of the arc 5 and decrease in the opticalconductors 1, 3 with an increase of the distance from the arc 5. Thebrightness of the radiated thermonic emission will likewise decreasewith an increase of the distance from the arc 5.

In the case when the ambient parameters have changed, an actualintensity distribution which deviates from the reference intensitydistribution will result for the preset discharge current. The dischargecurrent is varied with the aid of the controller 12 of the controldevice 7 until the actual intensity distribution at least approaches thereference intensity distribution. In the case of the same intensitydistribution, the same temperature distributions is then obtained withthe result that a splice with the previously defined optimum minimumlosses is attained.

In the case of the use of a color camera, the intensity distributionscan be stored in a wavelength-resolved fashion, and this permits aparticularly accurate control of the discharge current.

Two methods which manage with a black and white camera are particularlyeconomical with reference to the quantity of data to be stored.Gray-scale values are assigned to the intensity distributions in theblack and white camera which acts as the sensor 8.

In the first method, the gray-scale values are averaged in this caseover the entire window of the black and white camera, and only the meangray-scale value of the reference intensity distribution is stored inthe storage device 13 of the image evaluation unit 9. Given a highertemperature than envisaged, a higher mean gray-scale value of the actualintensity distribution is measured, and thereby the discharge current isappropriately corrected.

A second method with gray-scale values is illustrated in FIGS. 2a and 2b. In this case, a reference position x1 for a prescribed gray-scalevalue, which is represented here by the transition of white to lightgray, is stored as the reference intensity distribution. If, duringfurther splicing operations, the temperature in the example changes tohigher temperatures, the position with the prescribed gray-scale valuewill now occur at an actual position x2 according to FIG. 2b. Theoriginal temperature distribution is achieved in this case bycontrolling the discharge current and thereupon displacing the actualposition x2 in the direction of the reference position x1. It is alsopossible to pick up and store temporal sequences of the intensitydistributions and then compare them with one another during the splicingoperations. The temporal sequence of the recordings is triggered in thiscase by switching on the discharge current.

The result of this is an automated control, which is independent ofambient parameters, of a uniform temperature distribution duringsplicing of the optical conductors.

I claim:
 1. A method for splicing optical conductors, said methodcomprising creating an arc discharge between two electrodes, whichdischarge is controlled by a discharge current, using a preset dischargecurrent for striking the arc between said electrodes, measuring aspatially resolved actual intensity distribution of the thermionicemissions occurring during the process at the optical conductors,comparing a spatially resolved reference intensity distribution with themeasured distribution to determine a deviation therebetween, correctingthe discharge current if a deviation occurs to cause the actualintensity distribution to approach the reference intensity distribution,the improvements comprising assigning a gray-scale value to the actualintensity distribution and the reference intensity distribution,evaluating the gray-scale values along the direction of the axes of thetwo optical conductors, comparing a reference position in the directionof the two optical conductors for the prescribed gray-scale value withthe actual position of the gray-scale value of the actual intensitydistribution and when a deviation occurs, controlling the dischargecurrent so that the actual position approaches the reference position.2. A method according to claim 1, wherein the corrected dischargecurrent is stored as a preset discharge current for following splicingoperations.
 3. A method according to claim 2, wherein the actualintensity distribution and the reference intensity distribution arestored and compared in a wavelength-resolved fashion.
 4. A methodaccording to claim 3, which includes storing a temporal actual sequenceof the intensity distribution of the images of the ends during switchingon the discharge current, comparing temporal actual sequence with astored reference sequence of the intensity distribution to determine anydeviation therebetween, and controlling the discharge current when adeviation occurs so that the actual sequence at least approaches thereference sequence.
 5. A method according to claim 4, which includesapplying a discharge current to trigger the temporal actual sequence andthe reference sequence.
 6. A method according to claim 1, which includesstoring the actual intensity distribution and the reference intensitydistribution in a wavelength-resolved fashion.
 7. A method according toclaim 6, which includes storing a temporal actual sequence of theintensity distribution of the images of the ends, comparing the storedreference sequence of the intensity distribution with the temporalactual sequence on switching on of the discharge current to determine adeviation therebetween, and controlling the discharge current when adeviation occurs, so that the actual sequence at least approaches thereference sequence.
 8. A method according to claim 7, wherein thetemporal actual sequence and reference sequence are triggered byapplying the discharge current.
 9. A method according to claim 1, whichincludes storing a temporal actual sequence of the intensitydistribution of the images of the ends on switching on of the dischargecurrent and comparing the temporal actual sequence with a storedreference sequence of the intensity distribution to determine adeviation, if a deviation occurs, controlling the discharge current sothat the actual sequence at least approaches the reference sequence. 10.A method according to claim 9, wherein the temporal actual sequence andthe reference sequence are triggered by applying the discharge current.11. A method for splicing two optical conductors using an arc dischargebetween two electrodes, which is controlled by a discharge current,initiating the arc discharge with a preset discharge current, measuringa spatially resolved actual intensity distribution of the thermionicemission occurring in the process along the direction of the axes of thetwo optical conductors, comparing a spatially resolved referenceintensity distribution with the actual intensity distribution todetermine a deviation, correcting the discharge current if a deviationappears, so that the actual intensity distribution approaches thereference distribution, and storing a corrected discharge current as apreset discharge current for a following splicing operation.
 12. Amethod for splicing optical conductors according to claim 11, whichincludes averaging a gray-scale value over the image of the two opticalconductors to determine a mean gray-scale value for the referenceintensity distribution and a mean gray-scale value for the actualintensity distribution, storing the mean gray-scale value of thereference intensity distribution, comparing the mean gray-scale value ofthe actual intensity distribution to the mean gray-scale value of thereference intensity distribution to determine a deviation, if adeviation occurs, controlling the discharge current so that the meangray-scale value of the actual intensity distribution approaches themean gray-scale value of the reference intensity distribution.
 13. Asplicing device for splicing optical conductors, said device includingat least two electrodes, holding devices for two optical conductors, acurrent source for striking an arc discharge between the electrodes,said current source having a set point generator for the purpose ofsetting a preset discharge current, the improvements comprising a sensorfor detecting a spatially resolved actual intensity distribution alongthe direction of the axes of the two optical conductors occurring duringsplicing, a storage device for storing a spatially resolved referenceintensity distribution along the direction of the axes of the twooptical conductors, a comparator for comparing the actual intensitydistribution with the reference intensity distribution and a controllerfor correcting the discharge current.
 14. A splicing device according toclaim 13, wherein the sensor also detects the position of the opticalconductors in the holding devices.